First, I'm interested in fundamental questions concerning evolution in heterogeneous environments. We address these questions by studying theoretical (mathematical) models. In these models, we explore the simple idea that mutations may not only affect an organism's fitness in its current habitat, but could also alter its spatial range. Despite the simplicity of this idea, little has been done to establish minimal models of the emerging evolutionary modes, in which adaptation and range expansion go hand in hand. We have made some progress by analyzing stochastic models of populations evolving in source-sink ecologies or one-dimensional gradients – but many directions remain unexplored. The formalisms we employ in these projects are often borrowed from physics (stochastic processes, front propagation, first-passage theory) and the models tend to be strongly simplified. This project is supported by a NWO "Veni" grant.

Second, we aim to understand the growth of bacterial cultures on mixed-substrate media based on coarse-grained, systems-level constraints and principles. Recently, fundamentally new insights into the classical phenomenon of catabolite repression have thrown new light on the regulation of carbon catabolic processes in Escherichia coli. We have shown that these insights permit quantitative predictions of, among others, substrate consumption patterns and steady-state growth rates. This line of work originated during my postdoc with Prof. Terence Hwa at UC San Diego and the CTBP; the experiments required to fuel and test our models are performed in his lab.

Hermsen, R., Deris, J.B. & Hwa, T. (2012). On the rapidity of antibiotic resistance evolution facilitated by a concentration gradient. Proceedings of the National Academy of Sciences of the United States of America, 109, (pp. 10775-10780) (6 p.).